This invention relates to the field of ethylenically unsaturated polyester or vinyl ester systems which comprise the unsaturated polyester or vinyl ester resin and an unsaturated organic monomer such as styrene which serves as a solvent for the unsaturated polyester or vinyl ester resin and as a reactant to cure the unsaturated polyester or vinyl ester resin. These resin systems are used for laminating, coating, and gel purposes. When used for laminating, the resin systems are typically fiber reinforced, usually with glass fibers.
A well known problem in this art is that the organic monomer tends to volatilize in significant amounts into the workplace environment. Styrene, the most typical organic monomer, is volatile and a suspected carcinogen and there are regulations in place to reduce styrene emissions during the coating or molding processes in industry. Others have proposed replacing part of the organic monomer in order to reduce the volatiles. For example, see Smeal, et al., U.S. Pat. No. 5,500,171, assigned to Aristech Chemical Corporation, and other Smeal, et al., patents also assigned to that assignee, which disclose replacing part or all of the organic monomer such as styrene with a different organic monomer, for example a multifunctional (meth)acrylate such as ethylene glycol dimethacrylate or alkoxylated bisphenol-A diacrylate or dimethacrylate. Others have proposed epoxidized soy bean oil diacrylate and trimethylolpropane trimethacrylate, to be used together to replace part of the styrene.
Lee, U.S. Pat. No. 4,465,806, discloses a conventional unsaturated polyester resin wherein the usual styrene is replaced by a reaction product of a polyepoxy compound and acrylic or methacrylic acid which may be the diacrylate of a polyglycidyl ether of bisphenol-A, wherein a significant portion of the epoxy groups remain unreacted for use in the resin, and subsequently form pendant OH groups.
European Patent Application 0 234 692 discloses a molding resin, having a low residual monomer concentration in the final product, wherein dimethacrylates such as ethoxylated bisphenol-A dimethacrylate can be used to reduce the amount of residual styrene monomer in contained molding processes such as cell molding, compression molding, and sheet molding. See also Reid and Rex U.S. Pat. No. 5,202,366, which includes a low-profile additive in a similar composition.
Such prior compositions do reduce the volatile emissions, but suffer from one or more disadvantages with respect to crosslinked polyester properties, e.g., heat distortion temperature is reduced.
It is therefore an object of this invention to provide an unsaturated polyester or vinyl ester composition useful for laminating, coating, and gel applications, having lower than normal amounts of volatile unsaturated monomer without reducing heat distortion properties and other physical properties.
This object, and others which will become apparent from the following disclosure, are provided by the present invention which, in one aspect, comprises a composition useful as a gel coat, binder, or laminating resin comprising (A) unsaturated polyester resin which is the reaction product of one or more polyols and one or more ethylenically unsaturated polycarboxylic acids, anhydrides, or amides, and optionally one or more polyethylenically unsaturated monomers, and/or a vinyl ester resin, (B) a monomer which dissolves said polyester or vinyl ester resin selected from the group consisting of styrene, vinyl toluene, methyl methacrylate, N-vinyl pyrrolidone, ethylene glycol dimethacrylate and the dimethacrylate of alkoxylated Bisphenol A, and (C) a second monomer selected from the group consisting of metal salts of an alpha, beta-ethylenically unsaturated carboxylic acids.
In another aspect, the invention comprises a method of preparing a polyester or a vinyl ester gel coat, binder, or laminating resin from a composition comprising an unsaturated polyester resin which is the reaction product of one or more polyols and one or more ethylenically unsaturated polycarboxylic acids, anhydrides, or amides, and/or vinyl ester resin, and a first monomer selected from the group consisting of styrene, vinyl toluene, methyl methacrylate, N-vinyl pyrrolidone, ethylene glycol dimethacrylate and the dimethacrylate of alkoxylated Bisphenol A, the improvement comprising replacing in said composition a portion of said first monomer with a second monomer selected from the group consisting of metal salts of an alpha, beta-ethylenically unsaturated carboxylic acids, resulting in a higher heat distortion temperature property.
Another aspect of the invention is the molded laminates, binder, and gel coatings prepared by the method of the invention from the composition of the invention.